1. Field of the Invention
The invention relates to a fastening or anchoring of blades of a turbomachine by means of blade roots to the rotor or stator of the turbomachine.
2. Discussion of Background
Blade fastenings of this type are found, as a rule, on rotors of compressors or thermal turbomachines. They are known in large numbers from the prior art.
The blades are introduced with the blade root into a groove which is located on the rotor. The blade root serves in this case for the transmission of force and torque to the rotor.
For vibration damping, cover plates (shroud elements) are often attached to the tip of the blade or supporting wings within the blade.
This is described, for example, in German patent specification DE 1,159,965.
Austrian patent specification AT 254,227 also discloses a cover plate of a turbine or compressor blade ring, in which the cover plates are pressed against one another by the action of force. The arrangement leads to an elastic prestressing of the blade. This torsional prestress of the blade takes place between the cover plate and the blade root, but leads to additional load on the blade root and on the rotor. Since the forces which occur not only have to be absorbed by the blade, but also by the blade root and by the rotor, these have a correspondingly massive construction.
Spacers are often arranged between the individual blade roots of the turbine blades, which spacers are intended to absorb the forces and also serve for vibration damping. This is known, for example, from the patents U.S. Pat. No. 2,916,257 or else U.S. Pat. No. 3,734,645. Another moving-blade fastening is also known from European preliminary publication EP-A1-520,258. For the limitation of circumferential forces as a result of thermal expansions, longitudinal webs are provided between the moving blades.
Such prior art has the disadvantage, however, that the load is transmitted basically via the blade root to the rotor. This applies particularly to the abovementioned torsional moments. However, the relatively massive construction of the rotor and blade roots has adverse effects particularly on the width of the blade and blade root and of the wheel disk and consequently also on the entire length of the rotor. As a result of the higher root load, more cost-effective root designs (for example, hammerhead root, rider blade root) had to be dispensed with and, instead, there had to be recourse to more stable and more costly root forms (such as, for example, the insertion root).
The aim of the invention is to avoid the disadvantages mentioned. Accordingly, one object of the invention is to provide a novel fastening for blades of a turbomachine to a rotor or stator, by means of which fastening the torsional moments can be absorbed to an increased extent by the blade root or the root plate of the blade, while at the same time the rotor/stator and the blade root are relieved. Moreover, the overall length of the rotor/stator is to be shortened or, for the same length, the number of blade rows is to be increased and/or the use of cost-effective root connections is to be made possible.
According to the invention, after the installation of all the blades, the blades are contiguous to one another on the rotor or stator at the root plate and/or at the blade root completely or partially without play or with a prestress and arc therefore supported relative to one another with respect to torsional moments, the torsional moments which act at the root plates and/or at the blade roots being opposite to the torsional moments which act at the cover plate or at the supporting wing.
This embodiment has the advantage that torsional moments are no longer or only marginally absorbed by the rotor, but, instead, by the root plates and/or blade roots contiguous to one another, since a twisting of these two structural elements is prevented. By virtue of this measure, the blade root and also the rotor (or stator) can have a correspondingly smaller dimensioning, since relatively high forces no longer have to be absorbed at the rotor (stator)/blade-root contact face. Overall, therefore, the length of the rotor can be reduced. With the length of the rotor (stator) being the same, the number of blade rows and consequently also the efficiency can be increased.
Moreover, it is possible to use other root connections which could not be used with the previous technique. For example, a single-prong insertion root, a hammerhead root or an equivalent simple blade root can advantageously be employed. Such blade roots can be manufactured in a simple way and without great difficulty by means of known milling methods.
The root plate and possibly also the blade root have a bevel which is advantageously contiguous to a bevel of an adjacent moving blade, and therefore torsional moments are absorbed mutually at this point.